DNA Fluorescence Probes For The Detection Of Mercury Ion And Its Complexing Agent

Mercury is a highly toxic and widespread pollutant in the environment, whichcan cause serious and permanent damage to human body. Therefore, sensitive andselective mercury detection is very important for environment monitoring and foodanalyses.Nucleic acid probes with advantages of simple design, good stability and flexiblesignal mechanism make its broad space to used in pharmaceutical，environment，foodand clinical areas．In this research paper, we construct three DNA probes to detectmercury and its complexing agents, The contents of the thesis are as follows:1. Using G-quadruplex instead of traditional quencher, we developed a newmothod for the detection of mercury and cysteine. A T-rich sequence is labeled with6-carboxyfluorescein （FAM） at its5′-end, nearby the3′-end is a G-rich sequencewhich can form G-quadruplex structure instead of traditional quenchers. Uponaddition of Hg^2-, T-rich sequence is folded into a hairpin structure which lead theG-quadruplex near to the FAM, and the FAM is quenched by the G-quadruplexowning to photo-induced electron transfer between the dye and the G-quadruplex.This signaling mechanism makes it possible to detect Hg²⁺by fluorescencespectroscopy. The approach is sensitive and the detection limit is4nmol/L. Ourdesign is simple and cost-effective, and it is able to be used in the real system withlittle interference. Considering that cysteine is a strong binder of Hg²⁺, this methodwas further exploited as a cysteine detection method. The detection limit was85nmol/L.2. A simple and “Turn on” type iodide anion assay was developed, based on theinherent quenching ability of G-quadruplex and fidelity of the‘‘thymine-Hg²⁺-thymine’’ binding motif. A T-rich sequence is labeled with6-carboxyfluorescein （FAM） at its5′-end, nearby the3′-end is a G-rich sequencewhich can form G-quadruplex structure instead of traditional quenchers. Uponaddition of Hg²⁺, T-rich sequence fold into a hairpin structure which lead theG-quadruplex near to the FAM, and the FAM is quenched by the G-quadruplexowning to photo-induced electron transfer between the dye and the G-quadruplex.After the addition of iodide, the fluorescence of FAM recovered considering thatiodide can bind with Hg²⁺. The novel method for the determination of iodide has beendeveloped in linear range of50～500nmol/L, with the detection limit of30nmol/L. This proposed method is highly selective and other anions have no interfering effectson the determination, which has been successfully applied for analysis of realsamples.3. A simple detection of mercury ion and glutathione was developed, based onthe super fluorescence amplifer caplity of this β-cyclodextrin polymer to increase thefluorescence of the guest molecule. A T-rich sequence is labeled with pyrene at itsboth ends. After addition of β-cyclodextrin polymer, the fluorescence intensity ofpyrene was amplifered remarkably. In the precence of mercury ions, the T-richsequence is folded into a hairpin structure which lead the pyrene to form dimer out ofthe β-cyclodextrin polymer cavity. And then the fluorescence of pyrene was decreasedwith the addtion amout of mercury ions. The novel method for the determination ofmercury has been developed with a detection limit of8nmol/L. This proposed methodwas highly selective and other anions have no interfering effects on the determination,which was successfully applied for analysis of real samples.